1. Field of the Invention
The present invention relates to an offshore wind turbine comprising a tower, where a nacelle is arranged on top of said tower, said nacelle comprising a rotor with at least two rotor blades, said wind turbine further comprising subsystems for controlling the wind turbine, for converting and transforming the power generated by the wind turbine and for connecting the wind turbine to the overall electrical grid, said tower being connected to a transition piece or a foundation at a lower end, said connection being at a position above sea level, where said wind turbine at a level above sea level comprises at least one structure for storing at least one container, said container having the size and measures of a standard container and containing at least some of said subsystems for converting and transforming power generated by the wind turbine, where said structure is arranged on the side of the tower. The invention further comprises a method of manufacturing such a concrete structure for an offshore wind turbine.
2. Description of Related Art
It is well known that wind turbines now and then have to be repaired or that specific parts have to be changed. Many of the mechanical and also electrical parts are housed in the nacelle on top of the tower of the wind turbine. Ever since the wind turbines have been installed offshore there have been attempts to figure out a suitable way of hoisting equipment to and from the nacelle. This is a need seeing as there is a demand for a quick exchange of parts as the sea has to be pretty calm in order to be able to unload or load parts from a ship to or from a wind turbine.
This can, e.g., be done with a build-in hoist in the nacelle. The hoist can be used to lift parts from a ship to the nacelle, where the parts can be installed. From U.S. Pat. No. 6,750,559 B2 it is known to install a movable container underneath the nacelle, where said container is used for receiving and storing parts for the wind turbine. This solution features a build-in hoist in the nacelle.
Another known method is described in European Patent Application EP 1 240 426 B1, where some of the vital electrical components are arranged in a pair of containers on the side of the wind turbine tower and in a position well above sea level. In EP 1 240 426 B1 there is described a solution where standard containers via hoisting equipment on the tower are hoisted from a ship to a position underneath a protective cladding. In this solution there is provided access from the tower to the container and vice versa via a connecting channel comprising suitable sealing means. Access to the container is made possible via an opening in the sidewall of the container. In one of the described embodiments in EP 1 240 426 B1 the containers are hoisted to a position underneath the protective cladding and are subsequently displaced in a sideward direction against the tower and into a more closed shed, thus protecting the container and the connection between the tower and the container against the elements.
In European Patent Application EP 1 240 426 B1 as in the other known solutions, one or two containers are positioned underneath a support structure and are left hanging from said structure, while mounted to the wind turbine. A considerable drawback in such solutions is that the containers have to be accessed by installations, e.g., cables and/or personnel via corresponding openings in the sidewall of the wind turbine tower and of the container. Such openings have to be as small as possible as every opening in the structure weakens the strength in the tower. As the openings have to be very small and as space is rather limited, this is not the optimum solution. Further, it is quite a challenge to obtain a sealing between the hanging container and the tower that is sufficiently waterproof.
Another problem regarding offshore wind turbines is that they generally are subjected to more extreme environmental conditions than conventional onshore turbines, e.g., typhoon- or hurricane-type conditions including large waves. Wave run-up is a phenomenon wherein waves encountering a surface above the water level, e.g., the cylindrical surface of a wind turbine tower, will rise vertically along the surface to a maximum run-up height. In extreme wave conditions, such wave run-up may reach a height of 25 meters above normal sea level. Such potential run-up heights force wind turbine designers to increase height clearances for wind turbines above sea level to prevent any potential damage caused to rotor blades or to electrical systems provided at the exterior of the tower surface by such large run-ups.
European Patent Application EP 1 240 426 B1 describes a system wherein electrical subsystems such as switchgears or transformers are housed in containers suspended on the exterior of the wind turbine tower, a housing provided about the containers. However, such a housing only provides partial protection from the elements, and does not account for the damage which may be caused by wave run-up, wherein waves may impact on the wind turbine tower and on the containers from any possible angle and direction.
From European Patent Application EP 2 011 924 A2 a transition piece and a platform for a wind turbine, made from concrete, is known. The platform is resting on a recess at the top of the transition piece which is arranged on top of a monopile foundation. The tower of the wind turbine is fastened at the upper end of the transition piece. The platform disclosed in European Patent Application EP 2 011 924 A2 is a work platform used by workers when entering and leaving the wind turbine. No technical installations are situated on this platform and the reason for manufacturing said transition piece and platform in concrete is to avoid problem with corrosion. Further there is not arranged any beds for accommodation of containers comprising various electrical equipment for controlling the wind turbine.